Animation Nodes extra nodes Morph between two objects with particles
Note- Please watch the tutorials of Animation Nodes based particle-system for Blender2.79x and Blender 2.8x and Forces and other Group Nodes.

I am using Blender 2.79x for the morphing particles but you can also use the same node-tree in Blender2.8x. 



Edit:

Morphing particles between animated objects: 
For morphing, we need random points on the mesh of the object that we will use for the locations of particles. So, I have made a AN-Random Points on Mesh group-node to scatter random points on the mesh using BVH nodes. You can adjust the seed, Amount (in this case is total particles) and scale, 


I have also made a AN-Custom Delay Falloff group-node which has easy controls (similar to keyed particle-system) for morphing transition between objects,
 

Step-1: I have added the particle-emitter Object A (Cube, you can also use a separate object for particle-emitter) and Object B (Cylinder) with animation on xyz-rotation,



The Emitter has these settings:



Step-2: Then add the AN-Particle Input group node which gives the necessary outputs (particle-system, locations, etc) and Particles Output node then connect the particle-system input, and also disable the Always execution option in the N-panel,

(You can download extra Group Nodes if you need.)

Step-3: Now we have to find the points/locations on the mesh objects (Emitter and Target) using AN-Random Points on Mesh group-node and Amount is the total number of particles:


Step-4: For the morphing effect, we have to Mix points (on the mesh, mentioned in Step-3) using AN-Vector List Mixer with Falloff which works similar to Mix Vectors node. Now, we can control the transition with any Falloff node,


Step-5: We have the resultant locations (or Post-Locations, after doing Step-4) and Pre-Locations, so we can calculate the velocities of the particles using AN-Velocities From Locations group node then connect the Post-Locations and Velocities to the Particles Output node,


Step-6: This is the final step, add the Falloff node which will control the morph transition. I have used the AN-Custom Delay Falloff node and set the Start Frame = 1, End Frame = 200 and Delay = 0.01 (you can change accordingly, e.g., to add some frames stay on some object),


Step-7: We can easily extend this node-tree for three objects transitions, here the third object is Object C (Ico sphere),


Step-8: I have used the AN-3D Noise group-node to add turbulence effect to the particles, and using Interpolate-node I have limited the turbulence effect during the transition, (two objects),
 

For three objects,


Step-9: After the final transition, to make the interaction of particles with gravity, I have added the Force filed and enable the All field weights in the particle settings. Then connect the AN-Vector List Mixer with Falloff group-node after the final object (in this case is Object C) to off the effect of final transition object and its falloff parameter is controlled by AN-Custom Delay Falloff group-node:
 

Three objects morphing of particles and interaction with gravity, the final node-tree:


Blend File for Blender 2.79x:





Blend File For Blender 2.8x (required addon to bake Node-Based Particles):